Iguanodon
Iguanodon (meaning "Iguana tooth") is a genus of ornithopod dinosaur that lived roughly halfway between the first of the swift bipedal hypsilophodontids and the ornithopods' culmination in the duck-billed dinosaurs. Many species of Iguanodon have been named, dating from the Kimmeridgian age of the Late Jurassic Period to the Cenomanian age of the Late Cretaceous Period from Asia, Europe, and North America. However, research in the first decade of the 2000s suggests that there is only one well-substantiated species: I. bernissartensis, that lived from the Barremian to the early Aptian (Early Cretaceous) in Europe, between about 130 and 120 million years ago. Iguanodon's most distinctive features were its large thumb spikes, which were possibly used for defence against predators. Discovered in 1822 and described three years later by English geologist Gideon Mantell, Iguanodon was the second dinosaur formally named, after Megalosaurus. Together with Megalosaurus and Hylaeosaurus, it was one of the three genera originally used to define Dinosauria. A large, bulky herbivore, Iguanodon is a member of Iguanodontia, along with the duck-billed hadrosaurs. The taxonomy of this genus continues to be a topic of study as new species are named or long-standing ones reassigned to other genera. Scientific understanding of Iguanodon has evolved over time as new information has been obtained from the fossils. The numerous specimens of this genus, including nearly complete skeletons from two well-known bonebeds, have allowed researchers to make informed hypotheses regarding many aspects of the living animal, including feeding, movement, and social behavior. As one of the first scientifically well-known dinosaurs, Iguanodon has occupied a small but notable place in the public's perception of dinosaurs, its artistic representation changing significantly in response to new interpretations of its remains. Description Iguanodon were bulky herbivores that could shift from bipedality to quadrupedality.2 The only well-supported species, I. bernissartensis, is estimated to have weighed about 3 tonnes (3.5 tons) on average,3 and measured about 10 metres long (33 ft) as an adult, with some specimens possibly as long as 13 metres (43 ft).4 These animals had large, tall but narrow skulls, with toothless beaks probably covered with keratin, and teeth like those of iguanas, but much larger and more closely packed.2 The arms of I. bernissartensis were long (up to 75% the length of the legs) and robust,4 with rather inflexible hands built so that the three central fingers could bear weight.2 The thumbs were conical spikes that stuck out away from the three main digits. In early restorations, the spike was placed on the animal's nose. Later fossils revealed the true nature of the thumb spikes,5 although their exact function is still debated. They could have been used for defense, or for foraging for food. The little finger was elongated and dextrous, and could have been used to manipulate objects. The phalangeal formula is 2-3-3-2-4, meaning that the innermost finger (phalange) has two bones, the next has three, etc.6 The legs were powerful, but not built for running, and each foot had three toes. The backbone and tail were supported and stiffened by ossified tendons, which were tendons that turned to bone during life (these rod-like bones are usually omitted from skeletal mounts and drawings) Classification and origins Iguanodon gives its name to the unranked clade Iguanodontia, a very populous group of ornithopods with many species known from the Middle Jurassic to the Late Cretaceous. Aside from Iguanodon, the best-known members of the clade include Dryosaurus, Camptosaurus, Ouranosaurus, and the duck-bills, or hadrosaurs. In older sources, Iguanodontidae was shown as a distinct family.78 This family traditionally has been something of a wastebasket taxon, including ornithopods that were neither hypsilophodontids or hadrosaurids. In practice, animals like Callovosaurus, Camptosaurus, Craspedodon, Kangnasaurus, Mochlodon, Muttaburrasaurus, Ouranosaurus, and Probactrosaurus were usually assigned to this family.8 With the advent of cladistic analyses, Iguanodontidae as traditionally construed was shown to be paraphyletic, and these animals are recognised to fall at different points in relation to hadrosaurs on a cladogram, instead of in a single distinct clade.29 Essentially, the modern concept of Iguanodontidae currently includes only Iguanodon. Groups like Iguanodontoidea are still used as unranked clades in the scientific literature, though many traditional iguanodontids are now included in the superfamily Hadrosauroidea. Iguanodon lies between Camptosaurus and Ouranosaurus in cladograms, and is probably descended from a camptosaur-like animal.2 At one point, Jack Horner suggested, based mostly on skull features, that hadrosaurids actually formed two more distantly related groups, with Iguanodon on the line to the flat-headed hadrosaurines, and Ouranosaurus on the line to the crested lambeosaurines,10 but his proposal has been rejected. The cladogram below follows an analysis by Andrew McDonald, 2012. |2= }} }} }} }} }} }} }} }} }} }} }} Biology External links * [http://www.lhl.lib.mo.us/events_exhib/exhibit/exhibits/dino/man1825.htm Paper Dinosaurs, 1824–1969: 2. Mantell's Iguanodon Teeth, 1825], from Linda Hall Library. * The Bernissart Iguanodons (Iguanodon herd found in Belgium). * [http://www.dinodata.org/index.php?option=com_content&task=view&id=6718&Itemid=67 Iguanodon] DinoData. * [http://collections.tepapa.govt.nz/objectdetails.aspx?oid=212194&coltype=history&regno=gh004839 Mantell's Iguanodon tooth in the collection of the Museum of New Zealand Te Papa Tongarewa] Category:Cretaceous dinosaurs Category:Dinosaurs of Europe Category:Iguanodonts